The incorporation of manganese ions in nickel hydroxide is described in Power Sources 1966, Pergamon Press, pages 239 ff. Doping with manganese(II) ions leads to a product with a .beta.-Ni(OH).sub.2 structure, and oxidation with hydrogen peroxide leads to amorphous manganese(IV) products. Neither product exhibits any improvements in the electrochemical properties compared with undoped nickel hydroxide.
It is shown in the relatively old published German patent application P 43 23 007.5 that the incorporation of trivalent manganese in nickel hydroxide leads to markedly improved cycle stability and thus to increased utilization of the one electron stage with a simultaneous nickel saving. The product may be prepared by reaction of a solution containing Mn(III) and Ni(II) ions with alkali liquors. A disadvantage of this process is its requirement for the use of large quantities of mineral acids such as H.sub.3 PO.sub.4 or H.sub.2 SO.sub.4, the anions of which are required to stabilize the trivalent manganese in the salt solution. These or other suitable anions prevent premature decomposition of the Mn(III) by disproportionation. Moreover, the process requires large quantities of alkali liquors, associated with the production of neutral salts in more than stoichiometric quantities which have to be removed via the waste water.
The object of the present invention is to provide an environmentally acceptable process for the preparation of Mn(III)-containing nickel hydroxides.